In a typical cellular radio system, wireless terminals (also known as mobile stations and/or user equipment units (UEs)) communicate via a radio access network (RAN) to one or more core networks. User equipment units (UEs) may be, for example, mobile telephones (“cellular” telephones), desktop computers, laptop computers, tablet computers, and/or any other devices with wireless communication capability to communicate voice and/or data with a radio access network.
The radio access network covers a geographical area which is divided into cell areas, with each cell area being served by a base station, e.g., a radio base station (RBS), which in some networks is also called “NodeB” or (in Long Term Evolution) an eNodeB. A cell is a geographical area where radio coverage is provided by the radio base station equipment at a base station site. Each cell is identified by an identity within the local radio area, which is broadcast in the cell. The base stations communicate over the air interface operating on radio frequencies with the UEs within range of the base stations.
In some versions (particularly earlier versions) of the radio access network, several base stations are typically connected (e.g., by landlines or microwave) to a radio network controller (RNC). The radio network controller, also sometimes termed a base station controller (BSC), supervises and coordinates various activities of the plural base stations connected thereto. The radio network controllers are typically connected to one or more core networks, typically through a gateway.
Universal Mobile Telecommunications System (UMTS) is a third generation mobile communication system, which evolved from the Global System for Mobile Communications (GSM), and is intended to provide improved mobile communication services based on Wideband Code Division Multiple Access (WCDMA) access technology. The Universal Terrestrial Radio Access Network (UTRAN) is essentially a radio access network using wideband code division multiple access for user equipment units (UEs). The Third Generation Partnership Project (3 GPP) has undertaken to evolve further the UTRAN and GSM based radio access network technologies.
Specifications for Evolved Universal Terrestrial Radio Access Network (E-UTRAN) are ongoing within the 3rd Generation Partnership Project (3 GPP). Another name used for E-UTRAN is the Long Term Evolution (LTE) Radio Access Network (RAN). Long Term Evolution (LTE) is a variant of a 3GPP radio access technology wherein the radio base station nodes are connected directly to a core network rather than to radio network controller (RNC) nodes. In general, in LTE the functions of a radio network controller node are performed by the radio base stations nodes. As such, the radio access network of an LTE system has an essentially “flat” architecture comprising radio base station nodes without reporting to radio network controller nodes.
The evolved UTRAN comprises evolved base station nodes, e.g., evolved NodeBs or eNBs, providing user-plane and control-plane protocol terminations toward the UEs. The eNB hosts the following functions (among other functions not listed): (1) functions for radio resource management (e.g., radio bearer control, radio admission control), connection mobility control, dynamic resource allocation (scheduling); (2) mobility management entity (MME) including, e.g., distribution of paging message to the eNBs; and (3) User Plane Entity (UPE), including IP Header Compression and encryption of user data streams; termination of U-plane packets for paging reasons, and switching of U-plane for support of UE mobility. The eNB hosts the PHYsical (PHY), Medium Access Control (MAC), Radio Link Control (RLC), and Packet Data Control Protocol (PDCP) layers that include the functionality of user-plane header-compression and encryption. The eNodeB also offers Radio Resource Control (RRC) functionality corresponding to the control plane. The eNodeB performs many functions including radio resource management, admission control, scheduling, enforcement of negotiated UL QoS, cell information broadcast, ciphering/deciphering of user and control plane data, and compression/decompression of DL/UL user plane packet headers.
The LTE standard is based on multi-carrier based radio access schemes such as Orthogonal Frequency-Division Multiplexing (OFDM) in the downlink and SC-FDMA in the uplink. Orthogonal FDM's (OFDM) spread spectrum technique distributes the data over a large number of carriers that are spaced apart at precise frequencies. This spacing provides the “orthogonality” in this technique which reduces interference. The benefits of OFDM are high spectral efficiency, resiliency to RF interference, and lower multi-path distortion.
As noted above, in the E-UTRAN Radio Access Network scheme, the management of radio resource such as time, frequency and spatial resources takes place in the individual base stations (or cells). Each eNodeB base station therefore includes a Radio Resource Management (RRM) unit for performing management of radio resources. These RRM units typically operate independently from each other, except for very limited exchange of information, such as traffic load condition.
FIGS. 1A and 1B schematically illustrate a conventional wireless network 10. Referring to FIG. 1A, in a conventional wireless network 10, a base station 12 communicates with a core network 18 through a gateway 16. Communications between the base station 12 and the gateway 16 are carried over a transport network 20, which may include wired and/or wireless communication links. The base station 12 also communicates with one or more user equipment units (UEs) 14 through a radio access network (RAN 30). Signals, such as voice and/or data signals, transmitted by the UE 14 are carried over the RAN 30 to the base station 12, and then over the transport network 20 to the gateway 16, for transmission to the core network 18.
Referring to FIG. 1B, a conventional wireless network 10 may include a plurality of base stations 12 that provide radio communication services for a plurality of user equipment units (UE) 14 within their respective geographic service areas (cells). Each base station 12 includes an associated RRM unit 24, and each of the base stations 12 communicates with the core network through a gateway 16 via a transport network 20. At the base stations 12, data received from and to be transmitted to the User Equipment units (UE) 14 is transported to and from the core network through a transport network 20 that may include a variety of transport links 22, such as optical fiber, microwave and/or copper wires.
Conventionally, these various transport links 22 are point to point connections, as shown in FIG. 1B. Each base station 12 generates or consumes a certain amount of data that may vary as traffic condition changes over time. Thus, the point to point links 22 are designed to accommodate the peak data rates a base station generates or consumes.
The output of the RRM unit 24 in a conventional radio access network is a schedule, which typically defines an allocation of time, frequency and/or spatial resources to the UEs 14 in the system, and the Modulation and Coding Scheme (MCS) the given resource can support.
FIG. 2 illustrates hypothetical resource allocation schedules for three different cells, Cell 0, Cell 1 and Cell 2. For clarity of illustration, the spatial dimension is omitted from the schedules shown in FIG. 2. However, it will be appreciated that the spatial dimension could include, for example, a particular sector of a cell in which resources are allocated to a UE 14.
In the example shown in FIG. 2, three frequencies (f1 to f3) and four time slots (TS1 to TS4) are available for allocation to various UEs. For example, in Cell 0, UE0 is allocated frequency f3 for two time slots, TS1 and TS2, and is instructed to use modulation and coding scheme MCS1 within those resources. UE1 is allocated frequency f2 for two time slots, TS1 and TS2, and is instructed to use modulation and coding scheme MCS7 within those resources. UE2 is allocated frequencies f2 and f3 for one time slot, TS3, and is instructed to use modulation and coding scheme MCS2 within those resources, etc.
There is one such resource allocation schedule for the uplink (i.e., for communications from the UE 14 to the base station 12) and another for downlink (i.e., for communications from the base station 12 to the UE 14), since the transport resource for the two link directions is statically allocated in the conventional network.
As long as the transport network links 22 are dimensioned to carry the peak traffic that the base stations 12 in the RAN may generate, the transport and radio access networks operate independently. The designs of the two networks are also disjoint.
In practice, the traffic generated or consumed by base stations 12 may vary over time and locations as users move. Therefore, not all base stations 12 may be operating at a peak rate at a given point in time. The statically dimensioned transport network 20 is not very efficient, as there may be excess capacity that may not be fully utilized at any given time.